Pump control including a teeter valve



J. K. DOUGLAS PUMP CONTROL INCLUDING A TEETER VALVE Filed Nov. 5. 1954 June 9, 1959 FIG. I

INVENTOR JAMES K.DOUGLAS United States Patent PUMP CONTROL INCLUDING A TEETER VALVE James K. Douglas, Shorewood, Wis, assignor to The Oilgear Company, Milwaukee, Wis., a corporation of Wisconsin Application November 5, 1954, Serial No. 467,198

7 Claims. (Cl. 121-41) This invention relates to controls for pumps of the type having a displacement varying member which 18 shittable in either of two opposite directions to vary pump displacement and is prevented from moving in any other direction.

The type of control to which the invention relates in particular includes a control servo-motor for moving the displacement varying member in one direction, and opposed servo-rnotor for moving the displacementwarymg member in the opposite direction, means for continuously supplying the opposed servo-motor with motive liquid at a constant low pressure from a suitable source, and means including a normally closed control valve for connecting the control servo-motor to the same source of motive liquid and to exhaust selectively.

The source of motive liquid ordinarily is a gear pump which operates continuously. The liquid discharged by the gear pump in excess of requirements is exhausted through a relief valve but the resistance of the relief valve is so low and the volumetric capacity of the gear pump is so small relatively to the volume of liquid in the circuit and the reservoir of the main pump that the heat generated at the gear pump relief valve is readily dissipated.

The piston of the control servo-motor ordinarily has a pressure area about twice that of the piston of the opposed servo-motor so that, when the control valve is adjusted to connect the control servo-motor to the source of motive liquid, the control servo-motor will move the displacement varying member in one direction against the resistance of the opposed servo-motor, when the control valve is adjusted to connect the control servo-motor to exhaust, the opposed servo-motor will move the displacement varying member in the opposite direction and, when the control valve is closed, the servo-motors will hold the displacement varying member stationary.

Pumps provided with controls of the above type have been in extensive use for many years and are highly successful. However, it sometimes is necessary to shift the displacement varying member when the pump is creating an excessively high pressure. For example, if a ship is running fast and the heh'n is suddenly thrown hard over, the pump which energizes the steering motors will often have to create a pressure fifty percent in excess of the maximum pressure for which the pump was designed.

Since the resultant of the reactions to the pumping forces is normal to the bearings on which the displacement varying member moves, the pumping force reactions urge the displacement varying member against the bearings and thus increase the resistance placement varying member as the pump pressure rises.

In a pump provided with a control of the above described type, the maximum force available for moving the displacement varying member in the one direction is equal to the difference between the pressure areas of the two servo-motor pistons multiplied by the pressure acting thereon, the same force is available for moving the displacement varying member in the opposite direction if the pressure area of the opposed servo-motor to movement of the dis- 2,889,813 Patented June 9, 19 59 ice is one-half that of the control servo-motor piston, and

that force is not suificient to move the displacement vary- 5 main pump.

The present invention has as its primary object to increase the force available for moving the displacement varying member without increasing the size of both servomotors or increasing the gear pump pressure.

Another object of the invention is to normally maintain predetermined pressures in a control servomotor and in an opposed servomotor and to automatically vary the pressure in the opposed servomotor in an equal amount and in an opposite direction to any variation in pressure in the control servomotor.

According to the invention, the opposed servo-motor is provided with a piston the same size as the piston of the control servo-motor and the pressure in the opposed servomotor is varied inversely to variations in the pressure in the control servo-motor.

The invention is exemplified by the pump control shown somewhat schematically in the accompanying drawing in which the views are as follows:

Fig. 1 is an end view, partly in section, of a pump to which the invention has been applied.

Fig. 2 is in part a circuit diagram and in part a view illustrating a valve which varies the pressure in the opposed servo-motor inversely to variations in the pressure in the control servo-motor.

For the purpose of illustration, shown applied to a pump 1 of a sively used type. described in Patent to state herein that and carried by a casing 2 which is mounted upon a reservoir 3, that its mechanism includes a displacement varying member or slide block 4 which is shiftable transversely in a horizontal plane in respect to the drawing and is prevented from moving in any other direction,

the invention has been well known and exten- Since such a pump is illustrated and No. 2,227,814, it is deemed sufiicient that pump displacement is zero when slide block 4 is slide block 4 is offset inder 7.

a outer ends by cylinder heads 11 in its central or neutral position, and that the pump will discharge liquid through one and have liquid returned to it through the other of two pipes 5 and 6 in a direction and at a rate determined by the direction and distance from its neutral position.

Slide block 4 is adapted to be moved toward the left in respect to the drawing by a control servo-motor comprising a cylinder 7, which is formed in casing 2, and a piston 8 which engages slide block 4 and is fitted in cyl- Slide block 4 is adapted to be moved in the opposite direction by an opposed servo-motor comprising a cylinder 9, which is formed in casing 2, and a piston 10 which engages slide block 4 and is fitted in cylinder 9. Cylinders 7 and 9 are closed at their and 12 respectively. In a control such as that shown in Patent No. 2,227,- 814, the piston of the opposed servo-motor has an area only about one-half that of the piston of the control. servo-motor, as explained above, but in practice the two servo-motor cylinders are made the same size so. that area.

it has its mechanism arranged Within Liquid for energizing servo-motors 7-8 and 9- 10 is supplied by a gear pump which has been shown separate from pump 1 but actually it is driven in unison with pump 1 and arranged within casing 2 according to common practice. Gear pump 15 draws liquid through a channel 16 from reservoir 3 and discharges it into a channel 17. The liquid discharged by gear pump 15 in excess of requirements is exhausted through a relief valve 18 which enables gear pump 15 to maintain a constant low pressure, such as 130 p.s.i., in channel 17. The liquid discharged by gear pump 15 is often used for other purposes in addition to energizing the servo-motors.

Channels 16 and 17 are formed at least in part in casing 2 and extend from gear pump 15 downward through the bottom of casing 2 so that gear pump 15 can draw liquid from reservoir 3 through channel 16 and other channels can be connected to supply channel 17 such as a channel 19 which has one of its ends connected to channel 17 and its other end connected to an annular groove or port 20 formed in the wall of a bore 21 which is formed in cylinder head 11. Bore 21 is in axial alinement with a bore 22 extending through piston 8 which has an elongated hub formed on its outer end and provided with a port 23. The inner end of bore 22 communicates with the interior of casing 2 such as by means of one or more passages 24 formed in the inner portion of piston 8.

Flow of liquid to and from servo-motor 78 is controlled by a rotary follow-up control valve 28 which is clsely fitted in bores 21 and 22 and is provided on its outer end with a lever 29 for rotating it and for restraining it from axial movement.

Valve 28 is provided with an internal passage 30 having one end thereof in communication at all times with port 20 to which liquid is continuously supplied at a low pressure by gear pump 15 as previously explained. The other end of passage 30 opens into a spiral groove 31 which is formed in the peripheral surface of valve 28 at one side of port 23. Valve 28 has formed in its peripheral surface at the other side of port 23 a spiral drain groove 32 which opens into the inner end of bore 22.

The arrangement is such that, when the pumps are running and valve 28 is rotated through a limited angular distance in a clockwise direction as Viewed fi'om the right hand end of Fig. 1, groove 31 will open to port 23 and liquid will flow from port 20 through passage 30, groove 31 and port 23 into cylinder 7 and cause piston 8 to move slide block 4 toward the left until port 23 moves out of registry with groove 31 which will cut ofi flow of liquid into cylinder 7 and cause slide block 4 to stop. Slide block 4 is thus moved through a linear distance proportional to the angular distance through which valve 28 was rotated.

Conversely, when valve 28 is rotated in the opposite direction, groove 32 will open to port 23 and permit liquid to escape from cylinder 7 through port 23, groove 32, bore 22 and passage 24, thereby permitting servomotor 9-10 to move slide block 4 toward the right until port 23 moves out of registry with groove 32 which will cut oil flow of liquid out of cylinder 7 and cause slide block 4 to stop. Slide block 4 is thus moved through a linear distance proportional to the angular distance through which valve 28 was rotated.

The pump control thus far described is substantially the same as the control shown in Patent No. 2,227,814 except that the two servo-motors are substantially the same size instead of one being about twice the size of the other.

Flow of liquid into and out of servo-motor 910 is controlled by a teeter valve so called because it varies the pressure in cylinder 9 inversely to variations in the pressure in cylinder 7. The teeter valve comprises a plunger 33 having two spaced apart heads or pistons 34 4 and 35 formed thereon and closely fitted in a bore 36 which is formed in cylinder head 12 and has an annular groove or port 37 formed in the wall thereof and connected to cylinder 9 by a channel 38.

Bore 36 has a partition 41 closely and rigidly secured therein at the right of piston 35 and a piston 42 slidably fitted therein at the right of partition 41 with its right end exposed to any pressure in a chamber 43 which is coaxial with bore 36. Motion is transmitted between piston 42 and plunger 33 by a pin 44 which is fixed to piston 42 and has a close sliding fit in partition 41. Since in order to turn and grind plunger 33 it is necessary to form recessed centers in its ends, the right hand end thereof is drilled and tapped and a flat head cap screw is threaded into it to provide a flat surface for engagement with pin 44.

Movement of plunger 33 and piston 42 toward the left is limited by a socket head pipe plug 45 which closes the end of bore 36. Movement of plunger 33 and piston 42 toward the right is limited by a reducing bushing 46 which closes the end of chamber 43 and forms a part of a channel 47 which connects chamber 43 to servomotor cylinder 7 so that piston 42 is subjected at all times to the pressure in cylinder 7. The rate at which liquid can flow into and out of chamber 43 is limited by an orifice 48 formed in a socket head pipe plug 49 threaded into bushing 46.

That part of bore 36 between piston 35 and partition 41 communicates with servo-motor cylinder 9 through a passage 52 and an orifice 53 which is formed in a socket head pipe plug 54 threaded into passage 52 so that the right end of plunger 33 is subjected at all times to the pressure in cylinder 9. Bore 36 communicates at the left of piston 34 with a channel 55 which is connected to gear pump supply channel 17 so that the left end of plunger 33 and the left face of piston 34 are subjected to gear pump pressure, the space between pistons 34 and 35 communicates with a channel 56 which is connected to exhaust, and the space between partition 41 and piston 42 communicates with a channel 57 which is connected to exhaust. Channels 55, 56 and 57 are formed partly in cylinder head 12 and partly in pump casing 2 but only one end of each of the channels appears in the drawing because those channels are arranged in so many difierent planes and extend in so many different directions that they cannot readily be shown in the drawing. Therefore, channels 55, 56 and 57 have been shown connected to their destinations by dotted lines bearing the same reference numerals as the channels.

Piston 34 normally covers port 37 and it preferably is provided in its opposite edges with notches or slots 58 of such depth that the axial distance between the adjacent edges of slots 58 is the same as the length of port 37 so that a slight movement of plunger 33 in one direction or the other will provide a limited opening between port 37 and either pressure channel 55 or exhaust channel 56 and a greater movement of plunger 33 will provide a substantial opening.

Since the source or gear pump pressure P produces a force of predetermined value that tends to move plunger 33 in a direction to connect cylinder 9 to pressure P channel 55 and since the pressure in cylinder 9 and the pressure P in cylinder 7 both tend to move plunger 33 in a direction to connect cylinder 9 to exhaust, plunger 33 will automatically maintain the pressure in cylinder 9 at such a value that the sum of the pressures in cylinders 7 and 9 is equal to the gear pump pressure. That is, P =P +P so that the teeter valve it Will maintain in cylinder 9 a pressure which is equal to the ditierence between the gear pump pressure and the pressure in cylinder 7. Also, since the area of plunger 33 on which the gear pump pressure acts, the area of piston 35 on which the pressure in cylinder 9 acts and the area of piston 42 on which the pressure in cylinder 7 acts are all the same, plunger 33 tends to maintain thepressure in each of cylinders 7 and 9 equal to one-half the gear pump pressure until control valve 28 is rotated.

The arrangement is such that, when control valve 28 is rotated in a direction to open groove 31 to port 23, gear pump liquid will enter cylinder 7 and increase the pressure therein, thereby causing liquid to flow through channel 47 into chamber 43 and cause piston 42 to move valve plunger 33 toward the left to open cylinder 9 to exhaust channel 56 so that the pressure in cylinder 9 drops and permits servo-motor 7--8 to move slide block 4 toward the left and cause piston 10 to eject liquid from cylinder 9 to exhaust. If the pump is creating an excessive pressure and valve 28 is rotated far enough and quickly enough, the pressure in cylinder 7' will rise ot the full gear pump pressure and will extend into chambers 43 and cause piston 42 to move plunger 33 far enough to drop the pressure in cylinder 9 to zero so that servo-motor 78 can exert its full force without opposition by servo-motor 9-10.

As slide block 4 and piston 8 move toward the left, port 23 tends to move out of communication with groove 31 as fast as rotation of valve 28 opens groove 31 to port 23 and, since the force required to start slide block 4 moving is greater than the force required to keep it moving, as soon as slide block 4 starts to move the pressure in cylinder 7 and in chamber 43 will drop and permit the gear pump pressure to move valve plunger 33 toward the right and cause piston 34 to throttle the flow from cylin-; der 9 to such an extent as to maintain in cylinder 9 a pressure which is equal to the dilference between the gear pump pressure and the pressure in cylinder 7 and which prevents overrun of slide block 4. When slide block 4 has moved to a position determined by the position to which lever 29 was moved, it will stop at which time the gear pump pressure will move valve plunger 33 slightly farther toward the right to close port 37 so that slide block 4 is then held stationary by the liquid trapped in cylinders 7 and 9.

When control valve 28 is rotated in the opposite direction, the control will function in the above described manner but in opposite phase. That is, when valve 28 is rotated in a direction to open groove 32 to port 23, the pressure in cylinder 7 and in chamber 43 will drop and permit the gear pump pressure to move valve plunger 33 toward the right to open port 37 to channel 55. If pump 1 is creating an excessive pressure and valve 28 is rotated far enough and quickly enough, the pressure in cylinder 7 will drop to zero and the full power of servo-motor 910 will be available for moving slide block 4.

The slide block force previously available in controls of the same general type is thus doubled in a control embodying the present invention without increasing the stress on the pump casing, increasing the squeeze on the slide block or causing undue heating of the motive liquid.

While the two servo-motors have been shown arranged on opposite sides of the pump and the control servomotor has been shown provided with a rotary follow-up type of control valve, the two servo-motors may be arranged on the same side of the pump, the control servomotor may be provided with any other suitable type of valve and the control may be modified in various other ways and applied to other types of pumps without departing from the scope of the invention which is hereby claimed as follows:

1. A control for a pump having a casing and a member arranged within said casing and movable in opposite directions selectively to vary the displacement of said pump, said control comprising a first servo-motor carried by said casing and adapted when energized to move said member in one direction, a second servo-motor carried by said casing and adapted when energized to move said member in the opposite direction, means for transmitting motion from said servo-motors to said member, a. source of motive liquid for energizing both of said servotion to connect said channel to said passage, an exhaustchannel connecting said bore at the other side of said;

passage to exhaust, a second passage connecting said bore at the other end of said plunger to said second servomotor to enable the pressure therein to urge said plunger in a direction to connect said first passage to said exhaust channel, a third servo-motor engaging the other end of said plunger, and a channel connecting said third servo-motor to said first servo-motor to enable said third servo-motor to urge said plunger in the last mentioned direction with a force proportional to the pressure in said first servo-motor.

2. A control for a pump having a casing and a member arranged within said casing and movable in opposite. directions selectively to vary the displacement of said pump, said control comprising a first servo-motor carried by said casing and adapted when energized to move said member in one direction, a second servo-motor carried by said casing and adapted when energized to move said member in the opposite direction, means for transmitting motion from said servo-motors to said member,

a source of motive liquid for energizing both of said servomotors, means for connecting said first servo-motor to said source and to exhaust selectively and for cutting oif flow of liquid to or from said first servo-motor, a valve body arranged in a stationary position and provided with a bore, a first passage connecting said bore to said second servo-motor, a pressure channel connecting said bore at one side of said passage to said source, a valve plunger fitted in said bore and normally blocking the end of said passage and having one end thereof exposed to the pressure in said channel which urges said plunger in a direction to connect said channel to said passage, an exhaust channel connecting said bore at the other side of said passage to exhaust, a partition fixed in said bore beyond said plunger and dividing it into a valve portion and a servo-motor portion, a second passage connecting said,

second servo-motor to said bore between said plunger and said partition to enable the pressure in said second servomotor to urge said plunger in a direction to connect said first passage to said exhaust channel, a piston fitted in said servo-motor portion and provided with a pin which engages said plunger and is slidably fitted in said partition, and a channel connecting said end portion to saidfirst servo-motor to enable said piston to urge said plunger in the last mentioned direction with a force proportional to the pressure in said first servo-motor.

3. A control for a pump having a casing and a member arranged within said casing and movable in opposite directions selectively to vary the displacement of said pump, said control comprising cylinder means carried vby said casing, piston means fitted in said cylinder means and operatively connected to said member, said cylinder means and piston means forming servo-motor means having a first pressure chamber and a second pressure cham-- ber and adapted to move said member in one direction or the other in response to motive liquid beingsupplied to one or the other of said chambers, a source of pressure liquid connected to both chambers, a valve connected between said first chamber and said source and operable to connect said first chamber to said source and to exhaust selectively and to out 01f flow of'liquid to or from said first chamber, a valve body hydraulically connected to said second chamber and tosaid source and to exhaust, teeter valve means arranged in said body and normally blocking communication between said second chamber and said, source and exhaust and having afirst area exposed to the pressure of said source which produces a force urging said valve means in one direction, and said valve means also having second and third areas and said second area exposed to the pressure of one chamber of said opposed servomotors and said third area exposed to the pressure of the other chamber so that the resulting forces thereon are additive and urge said valve means in an opposite direction, whereby the valve means automatically maintains the pressure in the second chamber at a value that varies inversely with the pressure in the first chamber.

4. A control for a pump having a casing and a member arranged within said casing and movable in opposite directions selectively to vary the displacement of said pump, said control comprising cylinder means carried bysaid casing, piston means fitted in said cylinder means and operatively connected to said member, said cylinder means and piston means forming servo-motor means having a first pressure chamber and a second pressure chamber and adapted to move said member in one direction or the other in response to motive liquid being supplied to one or the other of said chambers, a source of pressure liquid connected to both chambers, a follow-up type valve connected between said first chamber and said source and exhaust and operable to connect said first chamber to said source and to exhaust selectively and responsive to movement of said member for cutting ofi flow of liquid into or out of said first chamber, a valve body hydraulically connected to said second chamber and to said source and to exhaust, teeter valve means arranged in said body and normally blocking communication between said second chamber and said source and exhaust and having three pressure areas the first of which is exposed to the pressure at said source for urging said valve means in one direction and the second and third of which are each equal to and opposite to said first pressure area, passage means connecting said second pressure area to said second chamber, and channel means connecting said third pressure area to said first chamber so that the pressures in said second and first chambers, respectively, act on said second and third pressure areas and urge said valve means in an opposite direction.

5. A control for a pump having a casing and a member arranged within said casing and movable in opposite directions selectively to vary the displacement of said pump, said control comprising cylinder means carried by said casing, piston means fitted in said cylinder means and operatively connected to said member, said cylinder means and piston means forming servo-motor means having a first pressure chamber and a second pressure chamber and adapted to move said member in one direction or the other in response to motive liquid being supplied to one or the other of said chambers, a source of pressure liquid connected to both chambers, a valve connected between said first chamber and said source and operable to connect said first chamber to said source and to exhaust selectively and to cut off flow of liquid to or from said first chamber, a valve body hydraulically connected to said second chamber and to said source and to exhaust, teeter valve means arranged in said body and normally blocking communication between said second chamber and said source and exhaust and having a first pressure area exposed to the pressure of said source for urging said valve means in one direction to open the communication between said second chamber and said source, and said teeter valve means also having second and third pressure areas connected to said second and said first chambers, respectively, and exposed to the pressures therein so that said second and third pressure areas aid one another in urging said teeter valve means in an opposite direction to close the communication between said second chamber and said source and to open a commu nication between said second chamber and said exhaust.

6. A control for a pump having a casing and a member arranged within said casing, said control comprising a cylinder means with opposed pistons fitted in said cylinder means in operative engagement with said member for moving it in opposite directions to vary the displacement of the pump, said cylinder means including a first pressure chamber for one of said pistons and a second pressure chamber for the second of said pistons, a source of pressure liquid, a valve connected between said source and said first chamber to connect it to said source and to exhaust selectively and to cut ofl flow of liquid to or from said first chamber, and a valve body having spaced first and second passages each connected to said second chamber and a third passage connected to said first chamber, means connecting said source to said valve body on one side of said first passage and means connecting said exhaust thereto on the other side of said first passage, and valve means having a land normally blocking said first passage and a first pressure area continuously exposed to said source to urge said land in one direction away from said first passage for connection to said source, said valve means having a second pressure area continuously exposed to the pressure in said second chamber by fluid admitted through said second passage to urge said land in an opposite direction for blocking said first passage, and a ram means disposed in said valve body and exposed to the pressure in said first chamber, said ram means being operatively connected to said valve means to cooperate therewith in urging said land in said opposite direction to block said first passage and to connect said first passage to said exhaust so that said valve means varies the pressure in said second chamber inversely to the pressure in said first chamber.

7. A control for positioning a member movable in opposite directions, said control comprising cylinder means, piston means fitted in said cylinder means and operatively connected to said member, said cylinder means having a first pressure chamber and a second pressure chamber adapted to move said member in one direction or the other in response to liquid under pressure being supplied to one or the other of said chambers, a source of pressure liquid connected to both said chambers, a control valve connected between said first chamber and said source and exhaust to selectively admit and cut off flow of fluid to or from said first chamber, a teeter valve including a body hydraulically connected to said second chamber and to said source and to exhaust and including valve means arranged in said body to normally block communication between said second chamber and said source and said exhaust, means applying a force of a predetermined value on said valve means for urging said valve means in one direction to open the communication between said second chamber and said source, said valve means having first and second pressure areas arranged in said valve body hydraulically connected to said first and second chambers respectively with the pressures therefrom aiding each other to urge said valve means in an opposite direction to close the communication between said second chamber and said source to open the communication between said second chamber and said exhaust, means operating said control valve to change the position of said member for a predetermined movement thereof to either admit pressure fiuid to said first chamber or exhaust fluid therefrom so that the change in pressure in said first chamber causes said teeter valve to correspondingly exhaust fluid from said second chamber or admit pressure fluid thereto; means operating said control valve as said member attains said changed position so that said control valve closes said first chamber to said source and exhaust and said teeter valve closes said second chamber to said source and exhaust when the pressures from both said chambers acting on said pressure areas of said teeter valve pro- 9 due: a force equal and opposite to said predetermined 2,038,272 force. 2,186,266 References Cited in the file of this patent 2,3 89,829

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